Effect Of Refinement Research Articles

A comparison study of the strengthening effect of carbon nanomaterial reinforcements in the 3D skeleton-reinforced copper matrix composites

The interfacial bonding and efficient load transfer are the research focus of the carbon nanomaterials (CNMs) reinforced metal matrix composites. In this study, special structured copper composites with CNMs distributing in the 3-D skeleton (CNMs/Cuf®Cu) were designed and prepared. The open cell copper foams reinforced by carbon nanotubes (CNTs), reduced graphene oxide (RGO) or CNTs-RGO hybrid were prepared by electrodeposition with enhanced mechanical strength and acted as the reinforcing skeletons, and the pure copper phase with good ductility and conductivity was continuously filled in the foam pores through powder metallurgy. The 3-D skeleton reinforcing structure, network structured CNTs-RGO hybrid, grain refinement effect and the disordered interface with Cu2O interface products synergistically cause higher load transfer efficiency and result in improved mechanical properties for the CNTs-RGO/Cuf®Cu composite, which shows the ultimate tensile strength (UTS) of 382 MPa, fracture elongation of 43 % and electrical conductivity of 93.26%IACS.

Integrated control mechanism of ultrasound and ZrO2 particles on differential microstructures for the wire arc additive manufacturing

ABSTRACT Inhibiting unhomogenised microstructure during the directed energy deposition process with the electric arc energy source (DED-Arc) has become a significant challenge. Ultrasonic vibration leads to the severe stirring of liquid metal and break down dendrites in the inner-layer zone, which promotes the formation of fine grains after rapid solidification. In contrast, the grain refinement effect is not obvious in the semi-melting zone. The addition of ZrO2 particles in the 2319 Al-Cu alloy during the DED-Arc process can drag and pin the grain boundary to prevent grain coarsening in the semi-melting zone. Under the integrated effect of ultrasound and particles, ZrO2 particles can be evenly distributed in different regions, which is beneficial to enhance the microstructure uniformity of the deposition layer and ultimately achieving significant improvement in mechanical properties. The intergrated effect of ultrasonic vibration and particles on strength and elongation reach 13.8% and 92.4%, respectively.

Improving the Mechanical Properties of Low‐Carbon Steel by In Situ Strain Aging

A novel continuous process that utilizes the concept of strain aging not only in the automotive industry but also in structural materials as a whole is developed. The principle behind achieving in situ strain aging is as follows. 1) Dislocations are generated through compressive deformation during continuous pressing. 2) The processing conditions at the strain aging temperature create a favorable environment for the diffusion of interstitial atoms, leading to the formation of Cottrell atmospheres. The in situ strain aging‐processed low‐carbon steel demonstrates a significant increase in strength compared to the unprocessed sample (increased yield strength by ≈37.6 MPa), which can be attributed to the strain aging effect, as well as the combined effects of grain refinement and pre‐existing dislocations. Additionally, the generation of dislocations during compressive deformation suppresses void nucleation during pre‐strain, preventing a loss of elongation (reduced uniform elongation by ≈1.5%). The in situ strain aging‐processed low‐carbon steel exhibits a superior strength–elongation combination compared to both the unprocessed low‐carbon steel and strain aging‐simulated counterparts obtained through tensile deformation.

Influences of Si and C addition on microstructure and mechanical properties of Fe2.5CoNiCu high-entropy alloy

To evaluate the role of non-metallic element (Si and C) on the microstructural evolution and mechanical properties of Fe2.5CoNiCu high-entropy alloys (HEAs), two series of Fe2.5CoNiCuSix (x=0.1−0.3, molar fraction) and Fe2.5CoNiCuCx (x=0.15−0.4, molar fraction) HEAs were prepared by vacuum induction melting. The results show that the amounts of C and Si additions significantly stimulate the transformation of BCC/FCC dual phases into a single FCC structure, and the microstructural evolution appears to be more strongly influenced by the C addition. The Fe2.5CoNiCuSi0.2 HEA presents high hardness (HV 439.5) and tensile strength (868 MPa), which is attributed to the solution strengthening and grain refinement effect. Both the hardness and strength of Fe2.5CoNiCuCx HEAs increase with the addition of C, due to the formation of carbides and solution strengthening. This demonstrates that adding non-metallic element (C or Si) is a viable approach for enhancing the strength and hardness of HEAs.

Phase field simulating grain refinement of magnesium alloy by thin strip second phase particles

The study has investigated the grain growth of AZ31 magnesium alloy matrix with fine strip second phase particles, by the phase field model in the real space and time, through introducing free energy equation, and compared with the simulated results containing spherical particles. The results showed that both the thin strip ellipsoidal particles and the cuboid particles have grain refinement effect on the microstructure, moreover, when the content of the second phase particles is the same, the refining effect of thin strip particles could be better than the spherical particles on the matrix microstructure. This study provides the real scale phase field models to research the grain refinement by second phase particles.

Phase transformation pathways in a Ti-5.9Cu alloy modified with Fe and Al

Titanium alloys have been gaining importance in various industries due to their advantageous combination of strength, low density, excellent corrosion/oxidation resistance, and superior mechanical properties at elevated temperatures. Recently, eutectoid Ti–Cu alloys have been explored as promising candidates for advanced processes. This work investigates the effects of Fe and Al on a Ti-5.9Cu alloy using multi-scale characterization techniques. While Fe acts as a β-stabilizing element (despite being a sluggish eutectoid former), Al acts as an α-stabilizer. This work focuses on the effects of combined addition of these elements, studied in different heat treatment conditions. The results show that a fine, equiaxed microstructure is obtained in the binary Ti-5.9Cu alloy, whereas the addition of 2 wt% Fe, or 2 wt% Fe combined with 2 wt% Al to the Ti-5.9Cu alloy deteriorates the effect of grain refinement and coarse, columnar grains result and a small amount of β-phase is retained. Further, the microstructure resulting from the eutectoid decomposition is altered dramatically from a lamellar pearlitic in the binary alloy to a lath-like α-phase with diverse decomposition products in the ternary and quaternary alloys accompanied by increasing hardness values. Evaluation of the α misorientation suggests that a substantial amount of non-Burgers α is present in the Ti-Cu alloy in contrast to the results of the ternary and quaternary alloys. The observed Cu-rich intermetallic compound was identified as Ti2Cu phase with off-stoichiometric composition. Results obtained explain how adding either Fe or Fe and Al leads to substantial hardening.

Achieving enhanced cryogenic toughness in a 1 GPa grade HSLA steel through reverse transformation of martensite

The effect of microstructure on crack resistance and cryogenic toughening in a 3.5 wt% Ni high-strength low-alloy (HSLA) steel was investigated. Multistage heat treatments involving quenching (Q), lamellarization (L), and tempering (T) were applied to prepare the HSLA steels with various microstructures, focusing on the reverse transformation and reconfiguration of martensite, as well as its influence on impact crack formation and propagation behavior by multi-scale characterizations. The results indicate that lamellarization treatment has little influence on tensile properties, but significantly improves impact toughness in the QL and QLT specimens, which exhibit over 30 % increment in Charpy V-notch (CVN) absorbed energy Et tested in range from RT to −196 °C, over 25 °C decrement in ductile-brittle transition temperature (DBTT), and much higher crack propagation energy Ep and higher ratio of Ep/Et, as compared with the as-quenched (AQ) and QT specimens. The lamellarization treatment also contributes to a significant refinement effect on martensitic block size, caused by fresh martensite transformation from the reversed austenite, resulting in an increment in high angle grain boundaries (HAGBs), with introduction of a small amount of retained austenite (RA) as well. Therefore, the impact crack resistance and cryogenic toughness is improved in specimens processed with lamellarization treatment, due to the enhancement in crack deflection and hindering effect of the HAGBs, as well as toughening effect by in situ austenite-to-martensite transformation of the RA. Based on the present study, a 1 GPa grade HSLA steel with high ductility and excellent cryogenic toughness can be produced.

Toughening mechanism and delayed fracture analysis of 4145H steel under intercritical quenching heat treatment process

Tuning thermal treatment schedule has been confirmed as an effective technical route for achieving optimum properties of steels. In the present work, the intercritical quenching tempering(IQT) process was applied to steel 4145H for oil drilling tools, and the performance enhancement and delayed fracture mechanism of the IQT process were comprehensively elucidated using multiscale characterization methods and various mechanical tests. Compared with the quenching and tempering(QT), the IQT process results in a separate island ferrite plus finely tempered sostenite organization, which reduces the dislocation density in the tempered organization and increases the proportion of recrystallized grains. Due to the grain refinement effect of multiple quenching, the pristine austenite grains were refined by 58 %. At the same time, the proportion of large-angle grain boundaries increased from 68.6 % to 80.3 %. The results of the mechanical property tests show that the intercritical 790 °C quenching treatment and tempering at 600 °C exhibits a tensile strength of 1087 MPa, a high elongation of 21.72 %, and a high impact work of 104 J compared to QT. The improved impact toughness is mainly attributed to the grain refinement effect of multiple quenching and the large-angle grain boundaries provided by the composite ferrite organization and M23C6 carbides. The impact of different ratios of large-angle grain boundaries on crack extension was also evolved by means of the crystal phase field, and the delayed fracture effect of large-angle grain boundaries was verified.

Quantitative hardness‐carbon content‐microstructure correlation in normalized plain carbon steel

AbstractComposition (carbon content) dependent critical structural evolution in correlation to hardness attained is judiciously investigated for plain carbon steel, the most widely used cost‐effective structural material, under normalizing treatment of industrial relevance involving non‐equilibrium still air cooling. The solid state phase transformation under non‐equilibrium still air cooling is conceived in terms of a logarithmic variation of eutectoid carbon content with the gross carbon content of steel in view of maintaining fixed maximum solubility of carbon in α‐iron with an assumption of the prevailing para‐equilibrium condition. Such a unique formulation for non‐equilibrium condition together with consideration of Hall–Petch type relationship and rule of mixture for two prime microconstituents (proeutectoid α‐ferrite and pearlite) finally results in a new mathematical relationship for chemical composition‐structure‐property correlation for the non‐equilibrium normalizing treatment readily practiced in industry. Indeed, a composition dependent structural refinement effect is established that is exemplified with the rise in hardness level in plain carbon steel under conventional normalizing treatment. Most importantly, the experimentally measured overall hardness values closely follow those obtained by the developed mathematical relationship, thereby meeting an ever‐needed requirement of direct determination of steel hardness of practical relevance from microstructural parameters.

Deformation behaviour, microstructure evolution and dynamic recrystallization mechanism of AZ31 magnesium alloy under co-extruded by Mg-Al composite billet

Conventional methods for hot extrusion of magnesium (Mg) alloy sheets have limitations for microstructure improvement and mechanical property enhancement. Co-extrusion of Mg alloy with an Al alloy core provides an opportunity for refining the grain size and improving basal texture. This study introduces a novel severe plastic deformation (SPD) method, Direct Extrusion-Continuous Shear (DE-CS), utilizing 6063 Al alloy as the core to fabricate innovative Mg/Al clad composite sheets. Monolithic Mg sheets (non-co-extruded condition) are extruded under identical conditions for comparison. By evaluating the microstructure and mechanical properties of AZ31 Mg alloy under co-extrusion and non-co-extrusion conditions, the positive effect of Mg-Al composite billet co-extrusion on AZ31 Mg alloy is established. The grain refinement effect in co-extruded samples is superior, enhancing plasticity without significant reduction in tensile strength. The microstructure evolution and dynamic recrystallization (DRX) behaviour of AZ31 Mg alloy during co-extrusion were analyzed comprehensively. The results indicate that, in the initial stages of deformation, various variants of {10−12} extension twins (ETs) play a crucial role in refining the original grains, forming initial [10−10]//ED fiber texture components alongside other non-basal components. Upon entering the shear deformation (SD) zone, deformed twins disappear, and small dynamically recrystallized (DRXed) grains emerge along boundaries of coarse deformation grains and within the grains. Strong shear deformations and compressive stress from transverse direction (TD) induce intensified prismatic <a> and pyramidal <c+a> slip, promoting continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX). CDRX predominantly affects elongated deformed grains, forming an [10−10]//ED fiber texture through high-energy grain boundary segmentation. Subsequently, compatible stress increases due to the activity of non-basal slip dislocation and the reduction in grain boundary (GB) size. DDRX emerges as the dominant mechanism, generating randomized [10−10]//ED fiber and non-fiber textures within parent grains and at boundaries.

Ultra-low thermal conductivity and improved thermoelectric performance in La2O3-dispersed Bi2Sr2Co2Oy ceramics

Thermoelectric materials are functional materials that directly convert heat energy and electric energy into each other. Nano-second-phase dispersion is an effective strategy to improve the energy conversion efficiency of thermoelectric materials through the energy filtering effect and the phonon scattering effect. In this study, the solid-state reaction method was used to prepare Bi2Sr2Co2Oy + l wt% La2O3 (l = 0.0, 0.1, 0.25, 0.5, 1.75) thermoelectric composites. An ultra-low thermal conductivity of 0.58 W/Km at 923 K was obtained by dispersing a small quantity of La2O3 as the nano-second-phase additive in the Bi2Sr2Co2Oy matrix. This was attributed to the increased hetero-interfaces and improved phonon scattering through the grain refinement effect. The dimensionless thermoelectric figure of merit (ZT) values of Bi2Sr2Co2Oy + 0.25 wt% La2O3 reached 0.28 at 923 K when their power factors were combined with littlechange, which was 21 % higher than that of the un-optimised pristine Bi2Sr2Co2Oy.

High‐resolution numerical simulations of polymer injection molding: Analysis of mesh size and refinement

AbstractAccurate and high‐resolution numerical simulations are crucial for preventing manufacturing defects during polymer injection molding. However, achieving efficient and precise simulations in this field remains a subject of ongoing research. In this study, we develop a macro‐scale numerical model to describe the behavior of melted polymer during the filling phase. Employing our in‐house finite‐element solver, XNS, we simulate the polymer and air flows as a two‐phase flow using the level‐set method. This formulation involves significant discontinuities across the interface, therefore a high mesh resolution along the interface becomes necessary. Furthermore, to accurately capture the polymer behavior along the wall, we apply a variable Navier slip condition that is dependent on the mesh size. To assess the impact of mesh size on the solution, we compare the results obtained with different levels of mesh refinement. Additionally, we investigate the effects of localized mesh refinement at the wall boundary and conclude that refinement in the interior of the channel is also required. Through our analysis, we highlight the importance of high‐resolution meshing and appropriate wall boundary conditions in achieving accurate simulations of polymer injection molding. This research contributes to the ongoing efforts in improving the understanding of the complex phenomena involved in this manufacturing process.

Effect of Repetitive Bending and Straightening Process on Microstructure Properties and Deformation Mechanism of a Ti-Al-Cr-Mo Alloy.

In this research, a repetitive bending and straightening process was carried out on the Ti-3Al-4Cr-Mo alloy for 20 passes. The changes in mechanical properties of the titanium alloy before and after repetitive bending and annealing were studied. The microstructure evolution and deformation mechanism were analyzed. The results show that after the repetitive bending and straightening process, the microstructure of the Ti-3Al-4Cr-Mo alloy is obviously refined, and, simultaneously, the yield strength is significantly improved. After annealing at 850 °C, the plastic ductility of the material was improved. The combined effects of grain refinement and dislocation behavior were the main reasons for the improvement in mechanical properties of the Ti-3Al-4Cr-Mo alloy. Twinning rarely occurred during plastic deformation of the Ti-3Al-4Cr-Mo alloy. The fine grains strongly inhibited the formation of twins. In addition, a small amount of α to β phase transformation was observed during the repetitive bending and straightening process of the material, which may have been induced by strain accumulation.

Designing grain refinement passes for multi-direction forging: A phase-field crystal study

Multi-directional forging is an effective plastic deformation method for polycrystalline grain refinement, and the degree of refinement is closely related to the number of forging passes. However, the relationship between the degree of refinement and the number of forging passes is almost ambiguous. Focusing on the forging passes, the grain refinement and dislocation nucleation mechanisms were revealed by combining the free energy variation and the strain field distribution using the dual-mode phase-field crystal model in our work. The results show that the nucleated dislocations within the grain can divide the grain into many finer grains under continuous stress. The nucleation mechanism of dislocation mainly includes two forms: grain boundary emission dislocation and atomic misalignment near the twin boundary. The strain field distribution reveals the mechanism of dislocation annihilation. The grain refinement effect of triple pass stress loading is the best, being 59 %, 18 %, and 43 % higher than that of the one forging pass, two forging passes, and four forging passes stress loading respectively. Moreover, the cause of the above phenomenon was further revealed by atomic analysis. This study reveals the response rule of forging passes to fine grain strengthening and gives feedback to guide the actual production experiment.

Effect of grain refinement on biomineralization and biodegradation of Mg–Ca alloy

Effect of grain refinement on biomineralization and biodegradation of Mg–Ca alloy

Al-20Si/Cu-8P high‑silicon aluminum alloy coating enhanced by laser remelting and refinement: Microstructure, mechanical properties and wear resistance

An Al-20Si/Cu-8P high‑silicon aluminum alloy coating was prepared on A356 aluminum alloy by plasma spraying and was remelted by laser technology subsequently. Whereupon, the microstructure, mechanical properties and wear resistance of the coating before and after remelting were comparatively studied, aiming to investigated the combined enhancement effect of remelting and refining on high‑silicon aluminum alloy coatings. The results showed that the laser remelting basically eliminated the defects in the sprayed coating, and produced a metallurgical bonding interface between the coating and the substrate. The microstructure of the coatings before and after remelting was both composed of primary silicon and eutectic structure (α-Al + Si). Nevertheless, the Cu8P dissolved more fully and dispersed more evenly in the remelted coating, which was conducive to fully utilizing its refinement effect on primary silicon. Thus, the primary silicon in the remelted coating was obviously reduced in size compared with that in the sprayed coating, and its distribution was more even. Accordingly, the hardness, elastic modulus and fracture toughness of the remelted coating were greatly enhanced compared with the sprayed coating. Under dry friction condition, the wear resistance of the two coatings was significantly superior to that of the substrate. Compared with the sprayed coating, the friction coefficient of the remelted coating was slightly smaller, and the wear volume was reduced by 33.1 %. Therefore, the microstructure of Al-20Si/Cu-8P high‑silicon aluminum alloy coating was significantly improved and its properties was obviously enhanced by laser remelting and refinement.

Effect of lithium anti-ablation and grain refinement introduced by TiC nanoparticles in LPBF Al–Li alloy

Al–Li alloys are extensively utilized in the field of aerospace due to their low density and high specific strength. However, laser powder bed fusion (LPBF) processed Al–Li alloys still encounter challenges because of hot cracking and Li element ablation. In this study, a TiC nanoparticle modified Al–Mg–Li alloy is developed for LPBF process. Full dense printed TiC modified Al–Mg–Li alloy can be obtained. The presence of TiC nanoparticles in the melt pool effectively increased the viscosity of Al alloy liquid, leading to a reduction in the metal vaporization and liquid spatters, thus preventing the Li ablation during LBPF. The Li content was significantly increased from 0.87 wt.% in the Al–Mg–Li alloy to 1.34 % in the TiC modified Al–Mg–Li alloy. Moreover, the TiC nanoparticles played a key role in transition of columnar to equiaxed grain. The average grain size of TiC modified Al–Mg–Li alloy was refined to about 1.5 μm, two orders of magnitude smaller than that in printed Al–Mg–Li alloy. A gradient transition reaction from TiC to Al3Ti was found on the TiC nanoparticles surface during LPBF. The in-situ formed Al3Ti phase on TiC nanoparticles significantly decreased the lattice mismatch with Al matrix, thereby resulting in an outstanding mechanical property of ultimate tensile strength of 343 MPa and elongation of 9.3 %. The effect of Li element anti-ablation induced by TiC nanoparticles provided a new pathway for additive manufacturing light-weight alloy.

Towards strength-ductility synergy in a weak-textured Mg–3Y extruded sheet via pre-twinning and annealing

Mg-RE (magnesium-rare earth) binary alloys, such as Mg–Y alloys, usually exhibit weakened texture and excellent plasticity compared with traditional RE-free Mg alloys. However, the weakened texture could lead to a significant decrease in the strength of Mg-RE binary alloys. In this work, the weak-textured Mg–3Y (wt. %) extruded sheet displayed good strength-ductility synergy with a 41% increase in the yield strength and a good ductility similar to the initial sheet via simple pre-twinning and annealing treatment (PT). After PT, the average grain size of the sheet decreased from 11.2 μm to 6.0 μm and 34.2% initial soft texture component (<11–21> //normal direction (ND)) was transformed into the hard texture component (<0001> //transverse direction (TD)). The effect of pre-twinning on deformation mechanisms was systematically investigated by slip trace analysis and activation stress (τ) analysis. Basal slip was the dominant deformation mechanism during the tension of the as-extruded (AE) specimen while pre-twinning promoted the activation of non-basal slip, especially prismatic slip in the PT specimen. The texture transformation and reduced critical resolved shear stress (CRSS) ratio between non-basal slip and basal slip induced by pre-twinning were primarily responsible for the high activity of non-basal slip. The underlying strengthening mechanism and the reason for good ductility were also rationally discussed. The strengthening effect of single grain refinement was relatively lower in the weak-textured Mg–3Y alloy. Texture hardening could effectively improve the effect of fine-grain strengthening. The excellent deformation compatibility between basal slip of parent grains and prismatic slip of twins as well as relatively higher activity of the second-order pyramidal slip was the origin of the good ductility of the PT specimen.

The novel strategy for enhancing mechanical properties and corrosion resistance via regulating multi-scale microstructure characteristics in Al-Si-Cu-Mg-Zr cast alloy

High strength and low corrosion resistance are always the contradiction in Al-Si-Cu-Mg cast alloy due to introducing high Cu and Mg levels. In this work, the new strategy was achieved for enhancing corrosion resistance and mechanical properties by regulating multi-scale microstructure characteristics in Al-9Si-4.2Cu-0.25Mg-Zr alloy. Electrochemical and corrosion morphology results indicate that the addition of Zr significantly enhances the corrosion resistance of the alloy. The grain refinement inhibits the charge transfer process between cathode phases and the matrix is the main reason at the Zr level of less than 0.15%. When the Zr level is up to 0.3%, the multi-scale synergistic effect of grain refinement and passive film enhancement significantly inhibits the corrosion process. Moreover, 0.3%Zr addition increases the yield strength to 419 MPa, tensile strength to 490 MPa, and the acceptable fracture elongation to 3.8%. The strengthening of mechanical and corrosion properties originates from the nano-Al3Zr precipitates after T6 treatment. This study provides a novel micro-mechanism and design strategy for simultaneously improving corrosion resistance and enhancing the mechanical properties of Al-Si-Cu-Mg cast alloy.

Texture weakening and grain refinement behavior of the extruded Mg-6.03Zn-0.55Zr alloy during hot plane strain compression

A series of hot plane strain compression (PSC) experiments of the extruded Mg-6.03Zn-0.55Zr alloy were conducted on the Gleeble-3500 machine with strain rates of 0.01 s−1 to 10 s−1 and temperatures ranging from 300 °C to 500 °C to reveal the microstructure evolution during the secondary process. The effects of grain refinement and texture modification which were easily affected by the deformation mechanism and dynamic recrystallization (DRX) were systematically studied. Experimental results showed that the main deformation mechanism during PSC was basal <a> slip (74.3 %–94.9 %) and assisted by prismatic <a> slip (4.8 %–21.1 %) and pyramidal <c+a> slip (0.3 %–4.6 %). Since the pyramidal <c+a> slip and prismatic <a> slip were more preferred to activate owing to the significant decrease of critical resolved shear stress (CRSS) at a higher temperature, the activation of non-basal slip promoted the c-axes of the grains deviated from compression direction which weakened the basal fiber texture. Moreover, the activation of non-basal slip could promote DRX behavior to some extent. Further analysis of the DRX mechanism showed that the continuous DRX (CDRX) by continuous rotation of low angle grain boundaries was dominant at lower temperatures and higher strain rates, while discontinuous DRX (DDRX) which nucleated at the grain boundaries played a more and more important role as the temperature increased and strain rate decreased. After characterizing the orientations of the DRXed grains, the CDRXed grains owned a similar grain orientation with the deformed grain while the DDRXed grains exhibited a fairly dispersed distribution, indicating that the weakening effect of the basal texture was greater with a higher DDRX fraction.